Make sure the item is checked in your render queue. If you start and cancel a render it will be added to your queue again but won't be checked. Best thing would be to clear the items in your render queue (select and delete) and then add it to the render queue again.
Just in case.. to add it: Make sure you're selecting the timeline window of the composition you want to render (there will be a yellow outline on the timeline panel). Go to Composition>Add to render queue.